1. Field of the Invention
The present invention relates to a communication system for communicating with mobile stations with radio signals, and particularly to a communication system which can prevent signals from colliding with each other between a paging control station of the system and base stations thereof to improve a signal traffic efficiency of the system.
2. Description of the Prior Art
A communication systems for communicating with mobil objects with radio signals is recently studied as a new radio communication system. For instance, a message communication system or an interoffice paging system is studied to transmit message data by using radio waves to mobile objects within particular areas of the office.
In such a communication system, a small area method or a minute area method is adopted to effectively use frequencies of radio waves and to cope with a weak electric field (weak power) of the radio wave.
FIG. 1 is a block diagram showing a conventional communication system for communicating with a mobile object. In the figure, base stations 31, 32, 33 and 34 are provided with small communication areas 35, 36, 37 and 38 respectively. The base stations are connected to a switching 20 with lines 50, 51, 52 and 53 respectively. Signals from a paging control station 2 are transmitted to the base stations 31, 32, 33 and 34 via the switching 20 and the corresponding lines.
This arrangement may be used to call a certain person. In this case, it is not clear in which area the person exists. Therefore, paging signals for calling the person shall be transmitted to all the base stations 31, 32, 33 and 34, and, to achieve this, the base stations shall have their respective lines 50, 51, 52 and 53 extending to the switching 20. This conventional system has, therefore, a drawback that, every time when an extension base station is added to the system, a new line shall be provided between the extension base station and the switching 20.